i almost always get money from KH and Ptolies for a ceasefire/alliance. i remember on one occasion got 10k. address KH after Sinope and Trapezund are yours. in most cases they are more than happy to end hostilities. Ptolies can fill your pockets with gold too since there is a common enemy nearby.
and those client rulers are a big time rip off. after i discovered the upkeep of almost $1000 i had to make sure mine is killed in the battle asap and dont ally with Sarmatians it might turn Armenians on you and you dont want that with the prospect of facing AS and possibly Ptolies, all and the same time.